Preprints
https://doi.org/10.5194/esurf-2021-92
https://doi.org/10.5194/esurf-2021-92
 
02 Dec 2021
02 Dec 2021
Status: a revised version of this preprint is currently under review for the journal ESurf.

Linking levee-building processes with channel avulsion: Geomorphic analysis for assessing avulsion frequency and style

Jeongyeon Han and Wonsuck Kim Jeongyeon Han and Wonsuck Kim
  • Department of Earth System Sciences, Yonsei University, Seoul, 03722, Republic of Korea

Abstract. A natural levee is a typical wedge-shaped deposit adjacent to a river channel. Given its location and distinctive features, the levee can serve as a key to revealing depositional processes of the coupled channel to floodplain system preserved in the rock record. Levee-floodplain topographic evolution is also closely linked to river avulsion processes which can spell a catastrophic flood. Nonetheless, the levee geometry and its aggradation pattern on the floodplain have not been fully incorporated in the study of avulsion. Here, we present a levee-building model using an advection settling of suspended sediment to reproduce the evolution of a fluvial levee over floods and to examine the effects of boundary conditions on levee geometry and grain-size trend. We further investigate river avulsion frequencies and styles (i.e., local vs. regional avulsion) associated with the grain-size distribution of supplied sediment and the overflow velocity into the floodplain, which control the levee geometry and especially the aggradation rate at the levee crest. In the modelling results, the levee develops 1) a concave-up profile, 2) exponentially decreasing grain size in the deposit, and 3) a relatively steeper shape for coarser sediment supply. The subsequent scaling analysis supports that the input grain size and levee profile slope are positively correlated with the avulsion frequency, whereas the overflow velocity is inversely proportional to the avulsion frequency. In connection with the avulsion styles and levee geometry, we suggest that steeper levee slopes tend to promote more local avulsions protecting abandoned channels from topographic healing, but gentler slopes of the levee are likely to lead to regional avulsions as abandoned channels with gentler levees are more vulnerable to the removal of topographic memory. The insights drawn from the current modelling work may thus have potential implications for reconstructing paleoenvironments in regard to river sediment transport and flood processes via levee deposits. Based on the roles of a levee on the avulsion frequency and style, the flood hazards triggered by river avulsions as well as the alluvial architecture in sedimentary records can be better assessed.

Jeongyeon Han and Wonsuck Kim

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on esurf-2021-92', Harm Jan Pierik, 13 Dec 2021
    • AC1: 'Reply on CC1', Wonsuck Kim, 01 Mar 2022
  • RC1: 'Comment on esurf-2021-92', Douglas Edmonds, 11 Jan 2022
  • RC2: 'Comment on esurf-2021-92', Anonymous Referee #2, 12 Jan 2022
  • AC2: 'Comment on esurf-2021-92', Wonsuck Kim, 01 Mar 2022

Jeongyeon Han and Wonsuck Kim

Jeongyeon Han and Wonsuck Kim

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Short summary
A levee-building model is presented to demonstrate the effects of flood conditions on levee slope, linking with river avulsion processes. Input grain size and levee slope are positively correlated with avulsion frequency, but overflow velocity is inversely related to it. High levee slopes develop local avulsions whereas low slopes develop regional avulsions. The link between the levee geometry and avulsion behaviours provides a better assessment of the flood hazards triggered by avulsion.